This invention relates to a spindle and hub assembly and more specifically to a spindle and hub assembly with an integrated motor for use in a disk drive.
Such integrated assemblies including spindle, hub, bearing and motor are commonly used in connection with magnetic or optical disk drives.
There are several kinds of integrated spindle and hub assemblies currently available on the market. One known assembly uses a bearing system with high precision ball bearings fitted into a hub, with the motor located in between the top and bottom bearings.
Due to increasing bit density required for disk drives, the precision required of spindle bearing assemblies for disk drives is constantly increasing. Ball bearings have the disadvantage of running with a very thin film of lubricant (in the order of 0.1-0.2 micrometers) between the balls and the bearing races while under operation. This very thin film causes extremely high pressures, and results in a lubricant film stiffness almost as high as the stiffness of the metal balls themselves. Surface imperfections on the balls limit the precision (normally measured in terms of "non-repeatable bearing runout") of the spindle since the ball and bearing race surfaces can more easily follow each others surface imperfections under operation.
Another known integrated spindle and hub assembly uses a journal-type hydrodynamic bearing with upper and lower thrust bearing, mounted into a hub. The hydrodynamic bearing is provided in the middle between the two thrust bearings. It requires a special ferrofluidic liquid responsive to a remote magnetic field, and has several disadvantages.
Due to the journal design there are a high number of parts and a high number of precision contact/mating surfaces which increase cost and can decrease yield. The journal design cannot compensate for variability of bearing stiffness with varying temperature. The hub forming the housing of this assembly is bell-shaped so that no symmetric design is attained. A further disadvantage is that the hub wall must be made very thin to accommodate the motor, thus increasing noise and vibrational problems. It is also difficult to seal the motor effectively with this configuration.
It is a primary objective of the invention to provide a high precision spindle and hub assembly for a disk drive which avoids the foregoing and other problems of known spindle and hub assemblies and which can be produced at low cost.